Deposition method and products

ABSTRACT

A method for producing a hard deposit on a substrate is described wherein a volatile halide of tungsten or molybdenum is reacted with a gas or gases containing hydrogen, oxygen and carbon to effect the deposition on a substrate of a compound of the metal in a liquid phase. The liquid phase deposited on the substrate is then reacted to remove oxygen and halogen and produce a hard deposit containing the metal and carbon. Also described are products which may be produced by the above method.

This is a continuation of application Ser. No. 702,436, filed July 6,1976 and now abandoned and which is a continuation-in-part ofapplication Ser. No. 588,391 filed June 19, 1975 and now abandoned,which was a continuation-in-part of application Ser. No. 358,110 filedMay 7, 1973, also now abandoned.

This invention relates to the production of hard deposits on substrates.More particularly, the invention relates to the production of depositson substrates as coatings, or the production of free standing objectsmade from a deposit after removal of a substrate. The deposits of theinvention have physical characteristics which are substantially improvedover those presently known to those skilled in the art.

The production of high hardness materials for wear or cutting purposeshas been approached in a variety of ways. High carbon steel has oftenbeen employed, frequently utilizing alloying ingredients such aschromium, vanadium, tungsten, molybdenum, cobalt, and others to improvehardness, toughness and strength at various operating temperatures. Castcobalt alloys, such as "Stellites" and similar materials, have also beenused for wear and cutting products. Another type of material has beencomposites of tungsten carbide or other carbides cemented with cobalt ornickel.

High carbon steel, with or without other alloying ingredients, hasexcellent bend strength, particularly at use temperature near roomtemperature, and quite high impact strength. High carbon steel, however,does not offer satisfactory hardness for wear-resistant and cutting toolproducts, its hardness being about Vickers number 900 (Vickers hardnessnumbers are in kg/mm² and are designated in the claims herein as VHN) ora Rockwell C hardness of about 65 to 70. Thus, high carbon and similartool steels have certain limits on their use.

Cast cobalt alloys, particularly those having high percentages of carbonand metal alloying species such as chromium, tungsten and others, havehardness values similar to those of high carbon steel. Moreover, theymaintain good hot hardness. However, these materials are more difficultto fabricate than high carbon steel, generally cost more, and are quitebrittle.

In order to overcome the physical and mechanical shortcomings of theaforementioned products and the difficulty in manufacturing them,attempts have been made to produce these materials by deposition. Highhardness materials are used as coatings on various types of substratesor are formed into free standing objects to produce wear parts or toolproducts. For example, commerically successful products having coatingsof titanium carbide over cemented tungsten carbide have been produced.Hardnesses of over 3000 Vickers with improved friction characteristicshave been achieved. By way of further example, some small diametertubing of tungsten carbide has been produced by deposition on a mandrelwhich is subsequently removed.

Deposits which have been produced commercially thus far, both forcoating substrates and for producing free standing objects, havesuffered certain drawbacks. Although hardness appears to be satisfactoryin some cases, the strength and toughness of the material has often beenlower than desired. Typically, such deposits have been produced bychemical vapor deposition techniques and have resulted in columnar grainstructures wherein the grain size is relatively large. Because of thegrain size and the columnar distribution of the grains, such depositshave tended to be relatively brittle and mechanically weak. Moreover,the production of hard coatings has generally required the use of arelatively high substrate temperature and relatively low deposition rateduring the chemical vapor deposition process.

It is an object of the present invention to provide an improved methodfor producing coated substrates and free standing hard metal products.

Another object of the invention is to provide coated substrates and freestanding hard metal products having improved physical characteristics.

Another object of the invention is to provide, on substrates, improveddeposits of superior strength and quality.

It is another object of the invention to provide coated substrates withthe coating having extremely high hardness and strength, and freestanding hard metal objects of great strength.

Other objects of the invention will become apparent to those skilled inthe art from the following description, taken in connection with theaccompanying illustrations wherein:

FIG. 1 is a schematic diagram of a chemical vapor deposition systemwhich may be employed in the practice of the method of the invention;

FIG. 2 is a photomicrograph at about 200 times magnification of a crosssection of a deposit produced in accordance with prior art chemicalvapor deposition techniques; and

FIG. 3 is a photomicrograph at about 500 times magnificationillustrating a cross section of a deposit produced in accordance withthe invention.

Very generally, the method of the invention comprises providing avolatile halide of tungsten or molybdenum. The volatile halide isreacted, off the surface of the substrate in the presence of a gas orgases containing hydrogen, oxygen, and carbon to form a firstintermediate compound of tungsten or molybdenum. The first intermediatecompound is reacted in the presence of gaseous hydrogen and one or moregases containing oxygen and carbon to cause the deposition on thesubstrate of a second intermediate compound of the metal which is in aliquid phase. (The term substrate is used herein in its broadest senseand is intended to include any form upon which the coating is deposited,whether subsequently used in the bonded condition or dispensed withafter deposition such as a mandrel or die.) The liquid phase secondintermediate compound is then reacted on the substrate surface toproduce a hard deposit containing tungsten or molybdenum and carbon.

Chemical vapor deposition, or CVD, is a well-known process for producinga coated substrate. In FIG. 1, one common apparatus is illustrated whichis used for coating a substrate 11, the latter being shown as agenerally cylindrical rod. The rod 11 is supported in a work holder orfixture 12 supported from a rod 13 resting on a disc shaped base 14. Thedisc shaped base 14 is supported on a reactor base 15 which is providedwith an annular groove 16 therein.

The reactor is completed by a heat proof cylindrical walled tube 17 ofquartz or similar material which seats in the annular groove 16 and issealed therein by an annular seal 18. The top of the quartz tube 17 isclosed by a rubber stopper 19 of conventional design removably securedtherein. There is, therefore, defined a reaction chamber 21 in which thedeposition process takes place.

In order to heat the substrate 11 to the desired temperature, as will beexplained, an induction heating coil 23 is provided surrounding theouter wall of the glass or quartz tube 17. The induction heating coil 23is supported by means not shown and is provided with leads 25 and 27 towhich the induction heating current is conducted from a suitable source,also not shown.

In order to regulate the pressure within the reaction chamber 21 andremoved reaction product gases, the lower wall or base 15 of the reactoris provided with an opening 29 therein through which a tube 31 ispassed. The tube 31 is suitably connected to a vacuum pump 33 and avacuum gauge 35 is connected in the line thereto for indicating thepressure within the chamber 21. By properly operating the vacuum pump33, the pressure within the chamber 21 may be regulated as desired.

A gas inlet tube 37 is provided in the rubber stopper 19 through acentral opening 39 therein. The tube 37 is connected through a pluralityof tubes 43, 45, 47 and 49 to regulator valves 51, 53, 55 and 57 andflowmeters 59, 61, 63 and 65, respectively.

Sources of reactant gas 67, 69, 71 and 73 are connected to theflowmeters 59, 61, 63 and 65, respectively, for introducing the desiredreactive gases for producing the chemical vapor deposition reactionswithin the chamber 21, as will be subsequently described.

A known method in which a coating of high hardness is produced on asubstrate by chemical vapor deposition involves the introduction to thereaction chamber 21 of a volatile compound of the metal species desiredin the deposit. Typically, this is a metal halide. This material, ingaseous form, is passed over a heated substrate, on which heated surfaceit is decomposed to deposit the metal of interest. A gaseous reducingagent, such as hydrogen, may be mixed with the volatile compound of themetal to assist in reducing it on the heated surface of the substrate.Other gaseous compounds may be added to the gas stream, such as carbonbearing gases, whereby compounds of the metal, such as carbides, areformed by chemical reaction on the heated surface. A more completeexplanation of the chemical vapor deposition process may be found inChapter 13 of the book "Vapor Deposition" edited by Powell, Oxley andBlocker, published by Wylie & Sons, 1966.

In FIG. 2, a cross sectional photomicrograph, magnified 200 times, showsa coated substrate produced by typical prior art CVD techniques, morespecifically set out in Example 3 below. The specimen was etched in amixture of dilute nitric and dilute hydrofluoric acid for about 30seconds at room temperature. It may be seen that the deposit iscomprised of relatively large columnar grains which are orientedperpendicularly of the substrate surface. Such deposits are typicallyquite brittle.

In each case involving the practice of chemical vapor deposition, effortis made to insure that the chemical reactions which cause the depositiontake place on the surface of the substrate. In other words, a reactionis caused which directly produces a solid deposit from the gaseousreactant or reactants on the surface of the substrate or mandrel.Heretofore, if the reaction was allowed to proceed in the gas streamaway from the heated surface, powdery non-adherent and non-coherentdeposits were made.

The method of the present invention, although similar to chemical vapordeposition, is not truly that. The method of the invention employs adeposition apparatus essentially similar to a chemical vapor depositionapparatus, however, the apparatus is operated in such a manner that thetypical chemical vapor deposition process does not take place.

In accordance with the method of this invention, a sequence of events ismade to take place which is different from what has been believeddesirable by those skilled in the art. It has been discovered thatsuperior deposits can be produced by causing a chemical reaction off ofthe surface of the substrate resulting in a first intermediate productin a gaseous phase. This product is further reacted to result in asecond intermediate product which is deposited on the substrate ormandrel in a liquid phase. The liquid phase on the substrate is furtherreacted to form the desired solid phase.

Such reactions may be possible with compounds of a number of metals,including the Group IVB, VB and VIB metals. However, the presentinvention is directed to producing a deposit comprised of tungsten ormolybdenum, and carbon. The general chemical characteristic required isthat the volatile halide of the metal portion of the compound must beable to be reacted off the surface of the substrate to produce a firstintermediate metallic compound in a gaseous or vaporous phase. Thisfirst intermediate compound must then be able to be reacted to form asecond intermediate compound having the proper vapor pressure andmelting temperature such that this second intermediate compound isdeposited on the substrate or mandrel as a liquid. The reaction toproduce this second intermediate and relatively non-volatile compoundmust be relatively fast. The compound must then be able to be convertedon the heated surface of the substrate by disproportionation or reactionwith a gaseous species, or both, to the desired solid deposit.

The first intermediate compound is produced off of the surface of thesubstrate and is observable as a fog or white halo slightly upstreamwith respect to the substrate. Raising the reactor temperature, however,can prevent visible formation of the fog although the reaction stilloccurs. Although not entirely understood, it is known that for thisreaction to take place, there must be present hydrogen and oxygen, andpossibly also carbon. The hydrogen should be in some other form thanpure hydrogen gas because pure hydrogen does not readily react at roomtemperature in the diatomic state. Pure hydrogen, however, is requiredfor the later reactions as explained below. The volumetric ratio of thetotal amount of hydrogen present to the volatile halide should be equalto or less than stoichiometric amounts. In other words, the ratio of theflow rate of hydrogen to the flow rate of the volatile halide should beequal to or less than the ratio of the number of gram atoms of hydrogento the number gram atoms of volatile halide in the balanced reaction. Athydrogen ratios higher than this, conventional chemical vapor depositiontends to take place, (i.e. direct deposition from the gaseous to thesolid phase) with the resultant brittle, columnar grained product.Preferably, the hydrogen to volatile halide volume ratio should begreater than about 0.5 to 1 for adequate yield in the reaction. Thefirst intermediate compound is believed to be some form of the metal inthe same valence state as it exists in the initial halide (for examplehexavalent tungsten).

The first intermediate compound is then reacted in the vicinity of thesubstrate surface due to the high heat of the substrate and the presenceof hydrogen. The result is the deposition on the substrate of a lowvapor pressure liquid in a very thin and highly viscous layer. Thenature of this liquid second intermediate compound is not understood,however, it is believed to be the metal in some intermediate valencestate combined with oxygen, carbon, or both, as well as a halogen. Forexample, the liquid may be an inorganic polymer. The liquid nature ofthe second intermediate compound is often apparent on the surface of thesubstrate during the deposition process. It is, however, believed thatthe liquid always forms even though not always easily observed.

The liquid second intermediate compound is then reacted to form thedesired solid deposit. This reaction is believed to involve reduction,disproportionation, or both. In any event, the oxygen and any remaininghalogen are removed, possibly by reaction with the hydrogen or merely bybeing carried away with the flow of the hydrogen. The resultant depositcontains the metal and at least about 0.1% and not greater than about 1%carbon by weight. The deposit is a very fine-grained, non-columnarstructure, often glass-like in appearance. Some layering is detectablein the deposit under high magnification and is believed to be related tovariations in the reaction rates relative to each other. It ispostulated that the fine-grained structure results from the extremelyrapid conversion of the intermediate liquid phase to a solid by chemicalreaction. X-ray diffraction analysis shows the deposit is akin totungsten but with a very finely dispersed carbide, probably in the formWC.

The carbon level is significant. Too much carbon results in a productwhich is too hard or too brittle. It is believed that all of the carbonexists in the deposit as a dispersed carbide. For higher quantities ofcarbide in the deposit, the hardness tends to increase, but at theexpense of also increasing the brittleness of the deposit. The totalvolume of the carbon bearing gases relative to the volatile halide ofthe metal serves to control the proportion of carbon in the soliddeposit. Too much carbon results in a brittle deposit. Too little carbonresults in the deposition of pure tungsten with columnar grains. It ispreferred, for the best operation of the process, that in the gas streamthe ratio of gram atoms of carbon to gram atoms of the metal should notexceed unity, and should be greater than 0.03 to 1.

The amount of carbon introduced is also dependent upon the oxygen in thesystem. Preferably, the ratio of gram atoms of carbon to gram atoms ofoxygen in the accumulation of gases introduced should not exceed a ratioof about 3 to 1. If this ratio is exceeded, too much carbon is presentin the system and the resultant deposit becomes too hard and brittle.

The preliminary reaction is caused to occur by reacting the volatilehalide of the metal with a gaseous substance containing hydrogen andoxygen. Elemental oxygen may be used or oxygen bearing volatilecompounds. In fact, it is most convenient to use a material whichcontains both carbon and oxygen since, when employed under properconditions, it can serve as both the source of oxygen for theintermediate liquid product and the source of carbon to form the finalsolid deposit. The suitable reacting gases, therefore, include volatilecompounds containing hydrogen, carbon and oxygen. Examples of the latterare alcohols such as methyl and ethyl alcohols, ketones such as acetone,ethers such as ethyl ether, and ethylene oxide.

In order to assure that a liquid phase is deposited on the substrate,the deposition temperature is held between about 650° C. and 1100° C.Too high a temperature volatilizes the liquid, whereas too low atemperature makes the reaction rate unacceptably low. Using the oxygenfrom one of the above reactants to form the liquid phase deposition, theconversion to the solid hard metal is accomplished by disproportionationor by reacting this liquid phase with hydrogen and one or more of thecarbon bearing gases. A combination of both reactions may actuallyoccur.

At higher temperatures in the aforementioned range, a lower hydrogenratio is required, and conversely, at lower temperatures, a higherhydrogen ratio is required. Lower operating temperatures than thespecified range typically result in deposits which are too brittle,whereas operating temperatures exceeding the specified range typicallyresult in columnar deposits or in non-adherent powder. The preferredoperating range is about 800° C. to 950° C. Since the reaction orreactions occurring are exothermic, heat builds up in the reactor veryquickly. If the reactor is too hot, the reaction which causes the firstintermediate compound to change to the second intermediate compound mayoccur off of the surface of the substrate, preventing deposition.

The operating pressure is preferably about 50 Torr or higher andsuccessful deposits have been achieved up to one atmosphere pressure.Typically, the higher the pressure, the higher the deposition rate. Iftoo low a pressure is used (or too high a temperature) the volatility ofthe liquid second intermediate compound may be exceeded, resulting in afailure of the deposition process.

The resultant thermochemically deposited product is substantially freeof columnar grains. An example is shown in FIG. 3, which is a depositproduced under the conditions set forth in Example 2 set out below. Thecross sectional photomicrograph was produced by etching in a mixture ofdilute nitric and hydrofluoric acids for about 30 seconds at roomtemperature. In the case of tungsten-carbon deposits, the Vickershardness number typically exceeds 1000 kg/mm² with a modulus of rupturein bending greater than 200 kg/mm² in the deposited and heat treatedcondition. The surface in the as-deposited condition is smooth and thegrain size is generally equal to or less than 5 microns, typically lessthan one micron, giving a glass-like or vitreous appearance.

As may be seen from FIG. 3, the deposit is laminar in appearance, withthe layers appearing to be of the order of 2000 A thick. Although notyet understood, it is believed these layers are caused by varyingconditions during deposition as evidenced by oscillating turbulence inthe fog or halo off the substrate. It is postualed that such layers havedifferent carbon content and may anneal at different rates duringdeposition. This may result in a complex internally stressed structurein which the layers closest to the substrate are prestressed to asubstantial degree of compression.

To assist in the understanding of the invention, certain samples of thedeposition techniques are given:

EXAMPLE 1

A 0.508 mm tungsten seed wire was used for a mandrel and heated by thepassage of current through the wire. The specimen temperature was heldat 950° C. Flows of gases were: tungsten hexafluoride, 350 ml/min,hydrogen 430 ml/min, argon 550 ml/min, and methanol, started at 70ml/min and increased regularly during the run to 100 ml/min. The totalpressure was 430 Torr. The deposition rate was 20 microns/min. The runtime was 17 minutes and 45 seconds. A white halo was observedsurrounding the substrate during deposition, indicating the presence ofthe first intermediate compound, and a liquid deposit on the substratewas continuously detectable, indicating the second intermediatecompound. The as-deposited material had a bend strength of 1,040 kg/mm²and a Vickers hardness number (500 gram weight) of 1,480 kg/mm². Themetallograph showed a lamellar deposit, like FIG. 3, with essentiallyabsence of columnar grains. The Youngs modulus of elasticity was 53,200kg/mm².

EXAMPLE 2

A 3 mm molybdenum rod was used for a mandrel heated to a temperature of960° C. at a reactor pressure of 400 Torr. The hydrogen flow was set at595 ml/min, a diluent flow of argon was set at 540 ml/min, a flow oftungsten hexafluoride was set at 740 ml/min, and a flow of dimethylether was set at 35 ml/min. A 0.45 mm deposit was produced on themandrel in 15 minutes. The deposit had very fine non-columnar grainstructure with a hardness of 1670 kg/mm² and a transverse rupturestrength of 295 kg/mm².

EXAMPLE 3

The same conditions stated in Example 2 were repeated except that a flowof 25 ml/min. of acetone was substituted for the dimethyl ether. A 0.9mm coating was deposited in twenty minutes and exhibited a Vickershardness of 1930 kg/mm² and a transverse rupture strength of 274 kg/mm².

EXAMPLE 4

The conditions of Example 2 were repeated using molybdenum hexafluorideinstead of tungsten hexafluoride and using methanol at 70 ml/min,instead of dimethyl ether. A 0.3 mm deposit was built up in 15 minutesand tested at a Vickers hardness number 1280 kg/mm² and a transverserupture strength of 253 kg/mm². In this case, as in the case of Examples2 and 3, the deposit was very fine grained and the grains werenon-columnar in their distribution.

EXAMPLE 5

The deposition experiment of Example 1 was rerun using identicalconditions except that methane was substituted for methanol inequivalent volumetric proportions. The methane contained the same amountof carbon but, of course, no oxygen. The resultant deposition was 0.375mm in thickness with a rough exterior surface showing tetragonal crystalfacets. The surface roughness was measured at approximately 64 rms. Themeasured hardness was 1380 kg/mm² and the bend strength 60 kg/mm². Theelastic modulus was unable to be measured because of the intrinsicbrittleness of the material. A heat treat at 1150° C. for 15 minutes didnot improve the strength of the material. No halo about the part wasobserved during deposition nor was any liquid on the surface of thesubstrate detectable during deposition. Metallographic examinationshowed a typical chemcial vapor deposition columnar deposit similar tothat shown in FIG. 2. Example 2 was clearly outside the limits of theinvention since there was no oxygen addition to effect the intermediateliquid deposit.

EXAMPLE 6

An experiment was conducted to compare the method of the invention withmore conventional CVD techniques. Tungsten hexafluoride was flowed overa 0.508 mm diameter molybdenum wire at a rate of 140 ml/min withhydrogen at a flow of 420 ml/min and carbon monoxide at a flow of 560ml/min. The wire was held at a temperature of 800° C. Depositionoccurred at a rate of 20 μ/min. No fog was observed in the chamber norwas any liquid apparent on the wire. Rather, a finely divided blackpowder was deposited on the chamber walls. The resultant deposit had afine-grained, dull, metallic appearance. A metallographic specimenshowed fine grain columnar crystals extending radially from the surfacewith some cylindrical rings superimposed. Hardness of the material was2,000 kg/mm² as measured with a 500 gram weight on a Vickers hardnesstester. Modulus of rupture in bending was 110 kg/mm². Failure on theBend Test was intergranular, i.e. as compared with the typical diagonal,or near axial breaks of samples by the method of the invention.

The tungsten-carbon deposits of the invention appear on the average tobe slightly harder than equivalent tungsten-carbide made by prior arttechniques. This is dependent, of course, on the ratios of metal tocarbon in the gas stream. At the highest preferred ratios, Vickershardness numbers of up to 2500 kg/mm² are achieved. In addition,unusually high bend strengths are achieved. Typical bend strengths forhot pressed tungsten carbide rarely exceeds about 50 kg/mm², whereas,tungsten-carbon deposits made by the method of the invention willfrequently exceed 300 kg/mm². This last strength number actually exceedsthe strength of cemented tungsten carbides. The unusual high stength isbelieved to be related directly to the fine grain laminar grainstructures such as illustrated in FIG. 3. The modulus of elasticitybefore or after heat treating is equal to or greater than 50,000 kg/mm².

It may therefore be seen that the invention provides an improved methodfor producing a coated substrate, as well as improved quality coatedsubstrates. The structure of the coating composition is such as toprovide superior physical qualities. More particularly, in the case oftungsten carbide deposits, the deposits are smooth surface fine grainedrandomly distributed crystals essentially free of columnar orientationand having a very high modulus of rupture. By subsequent heat treating,such tungsten carbide deposits may be almost doubled in their modulus ofrupture. Molybdenum-carbon alloy systems can also be effectivelyimproved in their deposit quality in accordance with the invention.Parameters necessary to do this are readily determinable by thoseskilled in the art from the information contained herein combined withthat contained in "Techniques of Metals Research", R. F. Bunshah, Ed.,Interscience Publishers, Div. of J. Wylie and Sons, New York, New York,1968, Volume 1, Chapter 33.

Various modifications of the invention in addition to those shown anddescribed herein will become apparent to those skilled in the art fromthe foregoing description and accompanying drawings. Such modificationsare intended to fall within the scope of the appended claims.

What is claimed is:
 1. A method for producing a hard deposit on asubstrate, comprising, providing a gaseous volatile halide of tungstenor molybdenum, reacting said volatile halide spaced from the surface ofthe substrate in the presence of an alcohol, ketone or ether to form afirst intermediate compound of tungsten or molybdenum which is spacedfrom the surface of the substrate, reacting said first intermediatecompound in the presence of gaseous hydrogen and one or more gasescontaining oxygen and carbon to cause the deposition on the substrate ofa second intermediate compound of tungsten or molybdenum which is in aliquid phase, and reacting the liquid phase second intermediate compoundon the surface of the substrate to produce a hard deposit containingessentially tungsten or molybdenum and carbon and having a modulus ofrupture in bending exceeding 200 kilograms per square millimeter.
 2. Amethod according to claim 1 wherein the hard deposit is essentiallytungsten and carbon.
 3. A method for producing a hard deposit on asubstrate, comprising, providing a gaseous volatile halide of tungsten,reacting said volatile halide spaced from the surface of the substratein the presence of an alcohol, ketone or ether to form a firstintermediate compound of tungsten which is in a gaseous phase spacedfrom the surface of the substrate, reacting said first intermediatecompound in the presence of gaseous hydrogen and one or more gasescontaining oxygen and carbon to cause the deposition on the substrate ofa second intermediate compound of tungsten which is in a liquid phase,and reacting the liquid phase second intermediate compound on thesurface of the substrate to produce a hard deposit containingessentially tungsten and carbon and having a modulus of rupture inbending exceeding 200 kilograms per square millimeter.
 4. A method forproducing a hard deposit on a substrate, comprising, placing thesubstrate in a chemical vapor deposition reactor and heating thesubstrate to a temperature of between about 650° C. and 1100° C.,providing a flow in the reactor of a gaseous volatile halide of tungstenor molybdenum, providing in the reactor a flow of hydrogen and of agaseous alcohol, ketone or ether and controlling the relative amounts ofvolatile halid, hydrogen, oxygen, and carbon, the substrate temperatureand the reactor pressure to form a gaseous compound of tungsten ormolybdenum which is spaced from the surface of the substrate and tocause the deposition on the substrate of a compound of tungsten ormolybdenum which is in a liquid phase and a subsequent conversion ofsaid liquid phase to a hard deposit containing tungsten or molybdenumand carbon and having a modulus of rupture in bending exceeding 200kilograms per square millimeter.
 5. A method according to claim 4wherein the ratio of hydrogen to the volatile halide is equal to or lessthan stoichiometric proportions.
 6. A method according to claim 4wherein the ratio of gram atoms of carbon to gram atoms of the tungstenor molybdenum in the gas stream does not exceed unity.
 7. A methodaccording to claim 4 wherein the ratio of gram atoms of carbon to gramatoms of oxygen in the gas stream does not exceed 3 to
 1. 8. A methodaccording to claim 4 wherein the temperature of the substrate ismaintained between about 800° C. and 950° C.
 9. A method for producing ahard deposit on a substrate, comprising, placing the substrate in achemical vapor deposition reactor and heating the substrate to atemperature not exceeding about 1000° C., providing a flow in thereactor of a gaseous volatile halide of tungsten, providing in thereactor a flow of hydrogen and a gaseous alcohol, ketone or ether,wherein the ratio of hydrogen to the volatile halide is equal to or lessthan stoichiometric proportions, wherein the ratio of gram atoms ofcarbon to gram atoms of tungsten does not exceed unity, and wherein theratio of gram atoms of carbon to gram atoms of oxygen does not exceed 3to 1, and controlling the relative amounts of volatile halide, hydrogen,oxygen, and carbon, the substrate temperature and the reactor pressureto cause the deposition on the substrate of a compound of tungsten whichis in a liquid phase and a subsequent conversion of said liquid phase toa hard deposit containing tungsten and carbon and having a modulus ofrupture in bending exceeding 200 kilograms per square millimeter.
 10. Amethod according to claim 9 wherein the flow of gases provided in thereactor includes hydrogen and methanol.
 11. A method for producing ahard deposit on a substrate comprising providing a gaseous volatilehalide of tungsten or molybdenum, reacting the volatile halide spacedfrom the surface of the substrate in the presence of gaseous hydrogenand ethyl alcohol, methyl alcohol, a ketone, or an ether to form a firstintermediate compound of tungsten or molybdenum which is spaced from thesurface of the substrate and to effect the deposition on the substrateof a second intermediate compound of tungsten or molybdenum which is ina liquid phase, and reacting the liquid phase deposit on the substratein the presence of gaseous hydrogen and ethyl alcohol, methyl alcohol, aketone or an ether to produce a hard deposit containing tungsten ormolybdenum and carbon and having a modulus of rupture in bendingexceeding 200 kilograms per square millimeter.
 12. A method according toclaim 11 wherein the volatile halide is reacted in the presence of asubstance selected from the group consisting of methyl alcohol, ethylalcohol, acetone, dimethyl ether, diethyl ether, and ethylene oxide. 13.A method according to claim 11 wherein the ratio of gram atoms of carbonto gram atoms of tungsten in the gas stream does not exceed unity.
 14. Amethod for producing a hard deposit on a substrate, comprising, placingthe substrate in a chemical vapor deposition reactor and heating thesubstrate to a temperature of about 650° C. to about 1100° C.,maintaining a pressure in the reactor of between about 50 Torr and oneatmosphere, providing in the reactor a flow of gaseous tungstenhexafluoride, gaseous hydrogen and a gaseous compound containing carbon,hydrogen and oxygen wherein the ratio of the gram atoms of the hydrogento gram atoms of tungsten hexafluoride is between about 0.5 to 1 and 3to 1, wherein the ratio of gram atoms of carbon to gram atoms oftungsten is between about 0.03 to 1 and about unity, wherein the ratioof gram atoms of carbon to gram atoms of oxygen is less than about 3 to1, and controlling the relative amounts of tungsten hexafluoride,hydrogen, oxygen and carbon, the substrate temperature in the reactorpressure to produce a deposit on the substrate containing tungsten and afinely dispersed carbide and having a modulus of rupture in bendingexceeding 200 kilograms per square millimeter.
 15. A method according toclaim 14 wherein the substrate temperature is between about 800° C. and950° C.
 16. A thermochemically deposited product consisting of a hardmetal alloy, primarily of tungsten and carbon, free of columnar grains,having a hardness of greater than 1000 VHN with a modulus of rupture inbending of greater than 200 kg/mm² in the deposited or deposited andheat treated condition, said product containing between about 0.1percent and one percent carbon finely dispersed in a form other than W₂C.
 17. A product according to claim 16 containing between about 0.1percent and one percent carbon as finely dispersed carbide in the formWC.
 18. A product according to claim 16 wherein the product is laminarin appearance when cross sectioned and etched, with layers of the orderof 2000 A thick.
 19. A product according to claim 16 having a grain sizeof less than one micron.
 20. A coated substrate comprising a substratehaving a coating thereon primarily of tungsten and carbon which isessentially free of columnar grains and which has a hardness greaterthan 2000 VHN, a grain size equal to or less than 5 microns, a modulusof rupture as deposited or as deposited and after heat treating equal toor greater than 200 kg/mm², a modulus of elasticity as deposited or asdeposited and after heat treating of equal to or greater than 50,000kg/mm², and a surface smoothness exceeding 4 rms in the as-depositedcondition, said coating containing between about 0.1 percent and onepercent carbon finely dispersed in a form other than W₂ C.
 21. A coatedsubstrate according to claim 20 wherein the coating has a grain size ofless than one micron.
 22. A coating substrate according to claim 20wherein the coating has a laminar appearance when cross sectioned andetched, with the layers having a thickness of the order of 2000 A.
 23. Acoated substrate according to claim 20 wherein the coating containsbetween about 0.1 percent and 1 percent carbon as a finely dispersedcarbide in the form WC.